Leukemia is the most common malignancy in childhood. Despite improved outcomes with combination chemotherapy regimens, significant challenges remain in the treatment of leukemia, especially in patients suffering from relapse or central nervous system (CNS)-positive disease. The bone marrow and CNS serve as sanctuary sites for leukemic cells during active chemotherapy, which can then relapse and spread to other organs. In particular, T-cell ALL (T-ALL), a sub-type of acute lymphoblastic leukemia (ALL), is an aggressive leukemia with a propensity to infiltrate the CNS. For these patients, new directions in the treatment options need to be explored. Approximately 60% of human T-ALL harbors a constitutively active protein, the Intracellular Domain of Notch1 (ICN1). Recently, in collaboration with Dr. Lan Zhou, we have established a disease model in which T-ALL harboring ICN1 mutation can be followed from pre-leukemia to full-blown leukemia in live mice. In collaboration with Dr. Letterio, the Huang lab have identified another signaling protein, Cdk5, as being important in the biology of leukemic cells and activated lymphocytes. Neither the contribution of Cdk5 to ICN1-induced T-ALL development, nor the role of Cdk5 as a therapeutic target in ALL has been explored. Here, we have assembled a team of scientists to study how Cdk5 affects ICN1-induced T-ALL tumorigenesis in the marrow and during CNS infiltration. We will study T-ALL development and their CNS seeding capacity by modulating Cdk5 activity in pre-leukemic lymphoblasts using lineage-specific Cdk5 genetic knockout strategies. A combination of cellular and molecular biology, immunology and application of our unique intravital two-photon microscopy capability - which allows the detection of dynamic individual pre- leukemic and leukemic cell behavior in the bone marrow and CNS of live mice - will be used to address these important questions. Coupled with drugs currently being tested against Cdk5 in Phase-I clinical trials, our investigations offer a new direction in the development of novel biological agents or immune-mediated therapies against T-ALL and CNS leukemia.